An innovative micro-scale approach for vulnerability and flood risk assessment with the application to property-level protection adoptions

Economic damage assessment for flood risk estimation is established in many countries, but attentions have been focused on macro- or meso-scale approaches and less on micro-scale approaches. Whilst the macro- or meso-scale approaches of flood damage assessment are suitable for regional- or national-oriented studies, micro-scale approaches are more suitable for cost–benefit analysis of engineered protection measures. Furthermore, there remains lack of systematic and automated approaches to estimate economic flood damage for multiple flood scenarios for the purpose of flood risk assessment. Studies on flood risk have also been driven by the assumption of stationary characteristic of flood hazard, hence the stationary-oriented vulnerability assessment. This study proposes a novel approach to assess vulnerability and flood risk and accounts for adaptability of the approach to nonstationary conditions of flood hazard. The approach is innovative in which an automated concurrent estimation of economic flood damage for a range of flood events on the basis of a micro-scale flood risk assessment is made possible. It accounts for the heterogeneous distribution of residential buildings of a community exposed to flood hazard. The feasibility of the methodology was tested using real historical flow records and spatial information of Teddington, London. Vulnerability curves and residual risk associated with a number of alternative extents of property-level protection adoptions are estimated by the application of the proposed methodology. It is found that the methodology has the capacity to provide valuable information on vulnerability and flood risk that can be integrated in a practical decision-making process for a reliable cost–benefit analysis of flood risk reduction options.     

Assessing flood hazard using flood marks and analytic hierarchy process approach: a case study for the 2013 flood event in Quang Nam,Vietnam

The production of flood hazard assessment maps is an important component of flood risk assessment. This study analyses flood hazard using flood mark data. The chosen case study is the 2013 flood event in Quang Nam, Vietnam. The impacts of this event included 17 deaths, 230 injuries, 91,739 flooded properties, 11,530 ha of submerged and damaged agricultural land, 85,080 animals killed and widespread damage to roads, canals, dykes and embankments. The flood mark data include flood depth and flood duration. Analytic hierarchy process method is used to assess the criteria and sub-criteria of the flood hazard. The weights of criteria and sub-criteria are generated based on the judgements of decision-makers using this method. This assessment is combined into a single map using weighted linear combination, integrated with GIS to produce a flood hazard map. Previous research has usually not considered flood duration in flood hazard assessment maps. This factor has a rather strong influence on the livelihood of local communities in Quang Nam, with most agricultural land within the floodplain. A more comprehensive flood hazard assessment mapping process, with the additional consideration of flood duration, can make a significant contribution to flood risk management activities in Vietnam.     

Evaluation of food risk parameters in the Day River Flood Diversion Area,Red River Delta,Vietnam

An interdisciplinary approach is necessary for flood risk assessment. Questions are often raised about which factors should be considered important in assessing the flood risk in an area and how to quantify these factors. This article defines and quantitatively evaluates the flood risk factors that would affect the Day River Flood Diversion Area in the context of integrated flood management in the Red River Delta, Vietnam. Expert analysis, in conjunction with field survey and Analytical Hierarchy Process (AHP), is applied to define and quantify parameters (indicators, subcomponents, and components) that contribute to flood risk. Flood duration is found to be the most prominent indicator in determining flood hazard. Residential buildings, population, and pollution are other fairly significant indicators contributing to flood vulnerability from the economic, social, and environmental perspectives, respectively. The study results will be useful in developing comprehensive flood risk maps for policy-makers and responsible authorities. Besides, local residents will also be able to implement suitable measures for reducing flood risk in the study area.     

Flood risk assessment using regional regression analysis

This study aimed to create a flood risk map for ungauged regions, which have limited flood damage data and other relevant data. The fact that there is a shortage of data that are critical for the establishment of a flood assessment and mitigation plan is not surprising even in developed countries like South Korea. To address this problem, the regional regression concept in statistical hydrology was introduced to the flood risk assessment field in this study, and it was framed with a series of two regression functions: flood damage and regional coefficients. As the second regression function utilizes the local socioeconomic variables, the resulting flood risk map can reflect the spatial characteristics well. The proposed methodology was applied to create flood risk maps for the three metropolitan areas in South Korea. The comparison of the proposed methodology with the existing methods revealed that only the proposed methodology can produce a statistically meaningful flood risk map based on a recent major flood in 2001.     

Large-scale assessment of flood risk and the effects of mitigation measures along the Elbe River

The downstream effects of flood risk mitigation measures and the necessity to develop flood risk management strategies that are effective on a basin scale call for a flood risk assessment methodology that can be applied at the scale of a large river. We present an example of a rapid flood risk assessment methodology for the Elbe River. A 1D hydraulic routing model is extended by including the effect of planned (regulated and unregulated) and unintended retention (dike breaches) on the peak water levels. We further add an inundation model for dike breaches due to dike overtopping and a macroscale economic approach to assess the flood damage. The flexible approach to model the effects of measures by means of volume storage functions allows for rapid assessment of combinations of retention measures of various proposed dimensions and at multiple locations. The method allows for the comparison of the flood risk at the scale of the main river trajectory, which has not been possible for the Elbe River to date. The model is applied to a series of exemplary flood risk mitigation measures to show the downstream effects and the additive effects of combinations of measures on the flood risk along the river. We further demonstrate the increase in the downstream flood risk resulting from unilateral decisions to increase the dike height at upstream locations. As expected, the results underline the potential effectiveness of increased retention along the river. The effects of controlled retention at the most upstream possible location and largest possible extent generate the most pronounced reduction of average annual damage. As expected, the effect of uncontrolled retention with dike relocations is significantly lower.     

Effect of uncertainty in land use, damage models and inundation depth on flood damage estimates

With the recent transition to a more risk-based approach in flood management, flood risk models—being a key component in flood risk management—are becoming increasingly important. Such models combine information from four components: (1) the flood hazard (mostly inundation depth), (2) the exposure (e.g. land use), (3) the value of elements at risk and (4) the susceptibility of the elements at risk to hydrologic conditions (e.g. depth–damage curves). All these components contain, however, a certain degree of uncertainty which propagates through the calculation and accumulates in the final damage estimate. In this study, an effort has been made to assess the influence of uncertainty in these four components on the final damage estimate. Different land-use data sets and damage models have been used to represent the uncertainties in the exposure, value and susceptibility components. For the flood hazard component, inundation depth has been varied systematically to estimate the sensitivity of flood damage estimations to this component. The results indicate that, assuming the uncertainty in inundation depth is about 25 cm (about 15% of the mean inundation depth), the total uncertainty surrounding the final damage estimate in the case study area can amount to a factor 5–6. The value of elements at risk and depth–damage curves are the most important sources of uncertainty in flood damage estimates and can both introduce about a factor 2 of uncertainty in the final damage estimates. Very large uncertainties in inundation depth would be necessary to have a similar effect on the uncertainty of the final damage estimate, which seem highly unrealistic. Hence, in order to reduce the uncertainties surrounding potential flood damage estimates, these components deserve prioritisation in future flood damage research. While absolute estimates of flood damage exhibit considerable uncertainty (the above-mentioned factor 5–6), estimates for proportional changes in flood damages (defined as the change in flood damages as a percentage of a base situation) are much more robust.     

Preliminary flood risk assessment: the case of Athens

Flood mapping, especially in urban areas, is a demanding task requiring substantial (and usually unavailable) data. However, with the recent introduction of the EU Floods Directive (2007/60/EC), the need for reliable, but cost effective, risk mapping at the regional scale is rising in the policy agenda. Methods are therefore required to allow for efficiently undertaking what the Directive terms “preliminary flood risk assessment,” in other words a screening of areas that could potentially be at risk of flooding and that consequently merit more detailed attention and analysis. Such methods cannot rely on modeling, as this would require more data and effort that is reasonable for this high-level, screening phase. This is especially true in urban areas, where modeling requires knowledge of the detailed urban terrain, the drainage networks, and their interactions. A GIS-based multicriteria flood risk assessment methodology was therefore developed and applied for the mapping of flood risk in urban areas. This approach quantifies the spatial distribution of flood risk and is able to deal with uncertainties in criteria values and to examine their influence on the overall flood risk assessment. It can further assess the spatially variable reliability of the resulting maps on the basis of the choice of method used to develop the maps. The approach is applied to the Greater Athens area and validated for its central and most urban part. A GIS database of economic, social, and environmental criteria contributing to flood risk was created. Three different multicriteria decision rules (Analytical Hierarchy Process, Weighted Linear Combination and Ordered Weighting Averaging) were applied, to produce the overall flood risk map of the area. To implement this methodology, the IDRISI Andes GIS software was customized and used. It is concluded that the results of the analysis are a reasonable representation of actual flood risk, on the basis of their comparison with historical flood events.     

National-scale Assessment of Current and Future Flood Risk in England and Wales

In recent years, through the availability of remotely sensed data and other national datasets, it has become possible to conduct national-scale flood risk assessment in England and Wales. The results of this type of risk analysis can be used to inform policy-making and prioritisation of resources for flood management. It can form the starting point for more detailed strategic and local-scale flood risk assessments. The national-scale risk assessment methodology outlined in this paper makes use of information on the location, standard of protection and condition of flood defences in England and Wales, together with datasets of floodplain extent, topography, occupancy and asset values. The flood risk assessment was applied to all of England and Wales in 2002 at which point the expected annual damage from flooding was estimated to be approximately £1 billion. This figure is comparable with records of recent flood damage. The methodology has subsequently been applied to examine the effects of climate and socio-economic change 50 and 80 years in the future. The analysis predicts increasing flood risk unless current flood management policies, practices and investment levels are changed – up to 20-fold increase in real terms economic risk by the 2080s in the scenario with highest economic growth. The increase is attributable primarily to a combination of climate change (in particular sea level rise and increasing precipitation in parts of the UK) and increasing economic vulnerability.     

A Probabilistic Modelling System for Assessing Flood Risks

In order to be economically viable, flood disaster mitigation should be based on a comprehensive assessment of the flood risk. This requires the estimation of the flood hazard (i.e. runoff and associated probability) and the consequences of flooding (i.e. property damage, damage to persons, etc.). Within the “German Research Network Natural Disasters” project, the working group on “Flood Risk Analysis” investigated the complete flood disaster chain from the triggering event down to its various consequences. The working group developed complex, spatially distributed models representing the relevant meteorological, hydrological, hydraulic, geo-technical, and socio-economic processes. In order to assess flood risk these complex deterministic models were complemented by a simple probabilistic model. The latter model consists of modules each representing one process of the flood disaster chain. Each module is a simple parameterisation of the corresponding more complex model. This ensures that the two approaches (simple probabilistic and complex deterministic) are compatible at all steps of the flood disaster chain. The simple stochastic approach allows a large number of simulation runs in a Monte Carlo framework thus providing the basis for a probabilistic risk assessment. Using the proposed model, the flood risk including an estimation of the flood damage was quantified for an example area at the river Rhine. Additionally, the important influence of upstream levee breaches on the flood risk at the lower reaches was assessed. The proposed model concept is useful for the integrated assessment of flood risks in flood prone areas, for cost-benefit assessment and risk-based design of flood protection measures and as a decision support tool for flood management.     

A multicriteria approach for flood risk mapping exemplified at the Mulde river,Germany

In this paper we develop a GIS-based multicriteria flood risk assessment and mapping approach. This approach includes flood risks which are not measured in monetary terms; it shows the spatial distribution of multiple risks, and it is able to deal with uncertainties in criteria values and to show their influence on the overall flood risk assessment. Additionally, the approach can be used to show the spatial allocation of the flood effects if risk reduction measures are implemented. The approach is applied to a pilot study for the River Mulde in Saxony, Germany, heavily affected by the hazardous flood in 2002. Therefore, a GIS database of economic, social and environmental risk criteria was created. Two different multicriteria decision rules, a disjunctive and an additive weighting approach, are utilised for an overall flood risk assessment in the area. For implementation, a software tool (FloodCalc) was developed supporting both, the risk calculation of the single criteria as well as the multicriteria analysis.

An integrated flood risk assessment model for property insurance industry in Taiwan

Taiwan is located in an area affected by Northwest Pacific typhoons, which are also one of the most important sources of rainfall to the island. Unfortunately, the abundant rainfall brought by typhoons frequently produces hazards. In recent years, typhoons and floods have caused serious damage, especially Typhoon Morakot in 2009. In this study, a probabilistic model is developed based on historical events which can be used to assess flood risk in Taiwan. There are 4 separate modules in this model, including a rainfall event module, a hydraulic module, a vulnerability module, and a financial loss module. Local data obtained from the Taiwan government are used to construct this model. Historical rainfall data for typhoon and flood events that have occurred since 1960, obtained from the Central Weather Bureau, are used for computing the maximum daily rainfall for each basin. In addition, the latest flood maps from the Water Resources Agency are collected to assess the probable inundation depth. A case study using the local data is carried out. Assessment is made to predict possible economic loss from different financial perspectives such as the total loss, insured loss, and loss exceeding probabilities. The assessment results can be used as a reference for making effective flood risk management strategies in Taiwan.     

GIS-based distributed technique for assessing economic loss from flood damage: pre-feasibility study for the Anyang Stream Basin in Korea

Large national budgets are required for flood damage reduction projects, making it critical to ensure that public money used therein be spent efficiently. Accordingly, reliable assessment of flood damage is a critical issue in analysis of the economic aspects of flood damage reduction projects. To this end, this study aims to provide a GIS (geographical information system)-based technique for distributed flood damage assessment. We consider two aspects of flood damage assessment from an engineering and economic perspective, i.e. flood inundation analysis and multi-dimensional flood damage analysis (MD-FDA). To perform this assessment, we used a GIS-based framework and data processing method to assess damages. The proposed methodology was applied to flood control channel projects for flood disaster prevention in the Anyang Stream Basin in Korea and presents detailed GIS data processing and assessment results. Findings from this study may contribute to the improvement of usability of MD-FDA and may provide research directions for integrating economic and engineering factors. This distributed technique will also assist in the decision-making process when evaluating the economic feasibility of flood damage reduction projects for structural and non-structural measures.     

The Effectiveness of Flood Damage Reduction Measures in the Montreal Region

The purpose of this study is to assess the effectiveness of two flood damage reduction measures – designation and dyking of floodplains. The study was carried out in four Quebec municipalities located on the shores of Lac des Deux-Montagnes and Riviére des Mille-Iles, namely Sainte-Marthe-sur-le-Lac, Saint-Eustache, Rosemére and Bois-des-Filion. Criteria for selecting the study areas were: area of the flood-risk zone, presence or absence of dykes, presence or absence of buildings, and availability of data. The study areas were selected with the help of flood risk maps of the Greater Montreal region. In each area, information on the number of buildings and their economic value was taken from the municipality's property assessment database. Trends in the occupancy and value of floodplains were identified and compared. The results of the study show that, as in other regions of Canada, flood damage reduction measures based on designation and mapping of floodplains have had no impact on occupancy, have failed to reduce flood damages, and have not even halted increases in such damages.     

Municipal flood hazard mapping: the case of British Columbia,Canada

Historical responses to flood hazards have stimulated development in hazardous areas. Scholars recommend an alternative approach to reducing flood losses that combines flood hazard mapping with land use planning to identify and direct development away from flood-prone areas. Creating flood hazard maps to inform municipal land use planning is an expensive and complex process that can require resources not always available at the municipal government level. Senior levels of government in some countries have addressed deficiencies in municipal capacity by assuming an active role in producing municipal flood hazard maps. In other countries, however, senior governments do not contribute to municipal flood hazard mapping. Despite a large body of research on the importance of municipal land use planning for addressing flood hazards, little is known about the extent of flood hazard information that is available to municipalities that do not receive outside assistance from senior governments for flood hazard mapping. We assess the status of flood hazard maps in British Columbia, where municipalities do not receive outside assistance in creating the maps. Our analysis shows that these maps are generally outdated and/or lacking a variety of features that are critical for supporting effective land use planning. We recommend that senior levels of government play an active role in providing municipalities with (1) detailed and current information regarding flood hazards in their jurisdiction and (2) compelling incentives to utilize this information.     

Simulation-based decision support system for flood damage assessment under uncertainty using remote sensing and census block information

The level of damage of flood events does not solely depend on exposure to flood waters. Vulnerabilities due to various socio-economic factors such as population at risk, public awareness, and presence of early warning systems, etc. should also be taken into account. Federal and state agencies, watershed management coalitions, insurance companies, need reliable decision support system to evaluate flood risk, to plan and design flood damage assessment and mitigation systems. In current practice, flood damage evaluations are generally carried out based on results obtained from one dimensional (1D) numerical simulations. In some cases, however, 1D simulation is not able to accurately capture the dynamics of the flood events. The present study describes a decision support system, which is based on 2D flood simulation results obtained with CCHE2D-FLOOD. The 2D computational results are complemented with information from various resources, such as census block layer, detailed survey data, and remote sensing images, to estimate loss of life and direct damages (meso or micro scale) to property under uncertainty. Flood damage calculations consider damages to residential, commercial, and industrial buildings in urban areas, and damages to crops in rural areas. The decision support system takes advantage of fast raster layer operations in a GIS platform to generate flood hazard maps based on various user-defined criteria. Monte Carlo method based on an event tree analysis is introduced to account for uncertainties in various parameters. A case study illustrates the uses of the proposed decision support system. The results show that the proposed decision support system allows stake holders to have a better appreciation of the consequences of the flood. It can also be used for planning, design, and evaluation of future flood mitigation measures.     

Estimation of structural vulnerability for flooding using geospatial tools in the rural area of Orissa,India

Vulnerability assessment of natural disasters is a crucial input for risk assessment and management. In the light of increasing frequency of disasters, societies must become more disaster resilient. This research tries to contribute to this aim. For risk assessment, insight is needed into the hazard, the elements at risk and their vulnerabilities. This study focused on the estimation of structural vulnerability due to flood for a number of structural elements at risk in the rural area of Orissa, India (Kendrapara), using a community-based approach together with geospatial analysis tools. Sixty-three households were interviewed about the 2003 floods in 11 villages and 166 elements at risk (buildings) were identified. Two main structural types were identified in the study area, and their vulnerability curves were made by plotting the relationships between flood depth and vulnerability for each structural type. The vulnerability ranges from 0 (no damage) to 1 (collapse/total damage). Structural type-1 is characterized by mud wall/floor material and a roof of paddy straw, and structural type-2 is characterized by reinforced cement concrete (RCC) walls/floor and a RCC roof. The results indicate that structural type-1 is most vulnerable for flooding. Besides flood depth, flood duration is also of major importance. Houses from structural type-1 were totally collapsed after 3 days of inundation. Damage of the houses of structural type-2 began after 10 days of inundation.     

太湖流域应对特大洪水防洪工程效益模拟

防洪效益评估对防洪工程投资决策与减灾对策制定具有重要意义。建立集成了与太湖流域防洪效益评估相关的系列模型和方法,包括含降雨产流与平原净雨计算的水文分析方法、由河网水动力学模型和平原区域洪水分析模型组成的大尺度水力学模型、综合流域社会经济和淹没因素的洪灾损失评估模型。模拟了太湖流域遇特大洪水的灾害损失,开展了不同防洪工程应对流域性特大洪水减灾效益的预测分析。结果表明：1999年型200年一遇降雨将会给太湖流域造成高达568.29亿元的直接经济损失,外排动力增强30%至100%的防洪效益介于26.69亿元到45.70亿元之间,新建圩区、太浦河拓宽的防洪效益依次减小,而圩区泵排能力增加30%的防洪效益仅为0.65亿元。基于研究成果提出了增设外排泵站、加强圩区科学调度、通过保险分担风险等应对特大洪水的对策措施建议,为太湖流域特大洪水的防治提供支撑和参考。     

太湖流域应对特大洪水防洪工程效益模拟

防洪效益评估对防洪工程投资决策与减灾对策制定具有重要意义。建立集成了与太湖流域防洪效益评估相关的系列模型和方法,包括含降雨产流与平原净雨计算的水文分析方法、由河网水动力学模型和平原区域洪水分析模型组成的大尺度水力学模型、综合流域社会经济和淹没因素的洪灾损失评估模型。模拟了太湖流域遇特大洪水的灾害损失,开展了不同防洪工程应对流域性特大洪水减灾效益的预测分析。结果表明:1999年型200年一遇降雨将会给太湖流域造成高达568.29亿元的直接经济损失,外排动力增强30%至100%的防洪效益介于26.69亿元到45.70亿元之间,新建圩区、太浦河拓宽的防洪效益依次减小,而圩区泵排能力增加30%的防洪效益仅为0.65亿元。基于研究成果提出了增设外排泵站、加强圩区科学调度、通过保险分担风险等应对特大洪水的对策措施建议,为太湖流域特大洪水的防治提供支撑和参考。     

A simplified approach for flood vulnerability assessment of historic sites

In the last decades, floods have increased in frequency all over the world due to diverse phenomena such as climate change, extended urbanization, land use, etc. Their social, cultural, economic and environmental impacts have also grown significantly, highlighting the need for the development of further studies and improved methods to manage and mitigate flood risk, mainly in urban areas. Historic sites need particular attention in this field, not only because the high and irreplaceable cultural value of these areas, but also taking into account that the constructive typologies that they host are particularly vulnerable to natural hazards. In consequence of that, the analysis of the phenomena, the evaluation of their consequences and the adoption of adequate mitigation and preparedness measures are presently a fundamental societal challenge. Having this in mind, the present paper aims at proposing an innovative methodology focused on the assessment of flood vulnerability in historic sites through the evaluation of a set of exposure and sensitivity indicators. From the analysis of these indicators, it is possible to obtain a Flood Vulnerability Index capable of measuring the spread of flood vulnerability over an extended area. The historic centre of Guimarães, in Portugal, declared by UNESCO as a World Heritage Site in 2001, is used here as a pilot case study to apply and discusses the preliminary version of the approach. Although some improvements are still needed, this approach can be already used to provides preliminary vulnerability scenarios and to point the way to the definition of more efficient and customized strategies for managing and mitigating flood risk in historic sites. Moreover, with further improvements and calibrations resorting to larger and more diverse data, it will be possible to reduce some of the uncertainties currently involved in the assessment process and to make its application wider and more robust.

     

洪涝灾害风险评估与分区研究进展

在全球气候变化和城市化进程不断加快的背景下,城市洪涝灾害频发,造成严重的经济损失和人员伤亡问题。对近年来中国典型城市洪涝灾害进行系统整理介绍,说明洪涝灾害带来的人员伤亡和经济损失巨大。风险评估作为一种非工程性防洪措施,是城市洪涝风险管理的首要工作,精确、高效的把握洪灾过程等特征可以为防灾减灾工作提供科学依据。对城市洪涝风险评估与分区的概念和内容进行系统梳理,常用的风险评估方法有数理统计法、不确定性分析法、遥感影像评估法、指标体系评估法、情景模拟评估法；风险分区常用方法有阈值法、经验公式法和物理机制法。论述了城市洪涝风险评估与分区常用方法的应用范围、优缺点及其发展前景。